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US 4,357,182 AGranted
Chromization of steels by gas process
AssigneeCreusot-Loire
InventorRobert Leveque
Life of this patent
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Abstract
A process for the chromization by gas of steels containing more than 0.2% of carbon, consisting of three successive treatments, the chromization treatment proper employing a cement having a ferrochrome base containing between 1% and 3% of carbon, and preferably 2%. The process is particularly useful in the chromization of structural and tool steels.
Claims5
Method of chromization of steels containing more than 0.2% carbon, comprising the successive steps of
- (a) ionic nitriding of a surface layer having a thickness in the range of 100 to 350 microns, carried out in an atmosphere consisting of a mixture of nitrogen and hydrogen at a temperature in the range of 450.degree. to 650.degree. C. for a period in the range of 5 to 40 hours, so as to obtain between 1.5% and 2.5% of nitrogen in the nitrided layer;
- (b) chromization by gas, of a duration in the range of 5 to 30 hours and carried out at temperatures in the range of 850.degree. to 1100.degree. C., said chromization employing a cement having a ferrochrome base with a chromium content in the range of 50% to 75% with a grain size in the range of 0.5 mm to 4 mm, the ferrochrome having a carbon content of 1% to 3%;
- and
- (c) heat treatment comprising an oil quenching of the chromized piece, followed by tempering at a temperature in the range of 600.degree. to 650.degree. C., of a duration in the range of 30 minutes to 10 hours.
1 more element
Dependencies are inferred from the claim text.